The Central Bureau of Investigation (CBI) has filed charges against India's top mobile phone carrier, Bharti Airtel, as part of a broader case involving alleged irregularities in airwave allocations.

Two Vodafone-owned companies—Hutchison Max and Sterling Cellular—and former Telecom Secretary CBI Shyamal Ghosh have also been accused of criminal conspiracy and face charges under the Prevention of Corruption Act. Mr Ghosh has been charged with misusing his office to confer additional spectrum in sweetheart deals to telecom giants. The CBI says the country lost nearly Rs 846 crore as a result.

The charge sheet filed in a Delhi court today does not mention any executives.

A Bharti spokesman said he had no immediate comment, while a Vodafone India spokesman declined to comment.

Bharti has previously said it had complied with all rules. Bharti shares were down 2.2 per cent as of 1.56 p.m., underperforming the 0.8 per cent decline in the broader Nifty.

The CBI probe concerns alleged irregularities in allotting mobile spectrum in 2002 during the NDA government led by the Bharatiya Janata Party (BJP). At the time, Pramod Mahajan, now deceased, was Telecom Minister.

The investigation follows a scandal over airwave allocations in 2008 by then Telecom Minister A Raja, who was jailed for allegedly accepting kickbacks in return for assigning under-priced licenses to mobile phone operators for second-generation or 2G airwaves. The 2G scam, as it’s referred to, shook Dr Manmohan Singh’s government after the national auditor said it was worth Rs 1.76 lakh crore.

While monitoring the investigations into the 2G scam, the Supreme Court had asked the CBI to investigate any possible irregularities in the granting of mobile permits from 2001 to 2007, before the Congress-led UPA coalition came to power.